The disclosures of Japanese Patent Application Nos. HEI 11-22140 filed on Jan. 29, 1999, HEI 11-34266 filed on Feb. 12, 1999, HEI 11-34271 filed on Feb. 12, 1999, HEI 11-60341 filed on Mar. 8, 1999 and HEI 11-64880 filed on Mar. 11, 1999 including the specifications, drawings and abstracts are incorporated herein by reference in their entirety.
1. Field of the Invention
The present invention relates to an intake air control system for an internal combustion engine and, more particularly, to an intake air control system designed for engine starting operation in an internal combustion engine employing an electronically controlled throttle valve whose opening degree is set independently of a depression amount of an accelerator pedal.
2. Description of the Related Art
With the development of computer technology in recent years, there is proposed an electronically controlled internal combustion engine whose rotational speed is electronically controlled optimally. In an internal combustion engine having a throttle valve whose opening degree is electronically controlled, the opening degree of the throttle valve can be set regardless of a depression amount of an accelerator pedal.
In an electronically controlled internal combustion engine, since a fuel injection valve is attached to the interior of an intake passage in the vicinity of each combustion chamber, there is a possibility that fuel may not be atomized sufficiently at the time of engine starting operation. In order to prevent deterioration of startability of the engine in such a case, it has been proposed to reduce an amount of intake air and enhance a negative pressure in an intake pipe by closing the intake passage by means of an electronically controlled throttle valve at the time of engine starting operation, and to thereby promote atomization of fuel (as disclosed, for example, in Japanese Patent Application Laid-Open No. SHO 61-96147, Japanese Patent Application Laid-Open No. SHO 63-150445 and the like).
In the art disclosed in the aforementioned publications, the effect of reducing concentrations of emission substances (inhibiting unburnt hydrocarbon from being discharged) can be achieved through promotion of atomization of fuel. However, since the engine starting operation is performed with the throttle valve being completely closed, the amount of intake air becomes insufficient after the air downstream of the throttle valve has been consumed. This tends to cause deterioration of startability of the engine.
It is an object of the present invention to provide an intake air control system capable of holding an electronically controlled throttle valve completely open within such a range that an internal combustion engine does not fail to be started due to a deficiency in amount of intake air, and of achieving both reduction of concentrations of emission substances and improvement in startability of the engine, by opening the throttle valve at an appropriate timing after a full-closure state of the throttle valve at the time of engine starting operation, in the internal combustion engine having the throttle valve wherein a negative pressure in an intake pipe is increased by closing an intake passage at the time of engine starting operation so as to promote atomization of fuel.
In order to achieve the above-stated object, according to one aspect of the present invention, there is provided an intake air control system for controlling an amount of air supplied to an internal combustion engine by adjusting an opening degree of an electronically controlled throttle valve provided in an intake passage of the internal combustion engine, comprising a throttle valve controller that closes the electronically controlled throttle valve to its full-closure position when an ignition switch of the internal combustion engine is turned on and opens the throttle valve after air has been sucked into the internal combustion engine, and an air amount determiner that determines an amount of air used for combustion in the internal combustion engine. The throttle valve controller opens the throttle valve to a predetermined opening degree when the amount of air reaches a predetermined amount.
This construction makes it possible to perform opening control of the electronically controlled throttle valve at an appropriate timing. Therefore, the throttle valve can be held completely closed within such a range that the engine does not fail to be started due to a deficiency in intake air in the engine, and it is possible to achieve both reduction of concentrations of emission substances and improvement in startability of the engine.